Feed oscillation via variable pitch gears

ABSTRACT

A positive feed tool includes a motor, a power supply coupled to the motor to power the motor, a gear head and a spindle. The gear head is coupled to the motor and operated responsive to powering of the motor. The gear head includes a drive assembly and a feed assembly. The spindle is coupled to the gear head to enable the spindle to be selectively driven rotationally and fed axially based on operation of the drive assembly and the feed assembly, respectively. The feed assembly includes a feed rate oscillator having a spindle feed gear coupled to a differential feed gear. The spindle feed gear is coupled to rotate the spindle to selectively axially feed the spindle. The differential feed gear is selectively coupled to an input shaft turned by the motor. The spindle feed gear or the differential feed gear has a variable pitch diameter.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. patent application No.62/255,772 filed Nov. 16, 2015, which is expressly incorporated byreference in its entirety.

TECHNICAL FIELD

Example embodiments generally relate to power tools and, in particular,relate to positive feed tools that employ feed rate oscillation.

BACKGROUND

Power tools are commonly used across all aspects of industry and in thehomes of consumers. Power tools are employed for multiple applicationsincluding, for example, drilling, tightening, sanding, and/or the like.For some drilling and fastening operations, positive feed tools may bepreferred. Positive feed tools are often used to perform operations onworkpieces such as steel, aluminum, titanium and composites, and mayemploy a tool feeding mechanism that feeds a bit into the workpiece at acontrolled rate. Such tools are common in the aviation industry, andother industries in which precise drilling is needed in metallicworkpieces or other hard workpieces.

Drilling holes, and particularly drilling deep holes within workpiecesthat are hard, using conventional methods can typically produce longdrilled chips that are difficult to evacuate from the hole. These longchips are generated because the bit is fed into the workpiece at aconstant feed rate (e.g., 0.003 inches per revolution). The constantfeed rate means that the chips will have a constant thickness (i.e.,0.003 inches) that leads to a spiral shaped chip forming and growing asthe drilling operation proceeds. The chips may end up being multiplehole diameters long, and can cause chip packing. The chips can thereforecause additional torque to be required, and can lead to longer cycletimes and poor hole quality.

To address this issue, variation or oscillation of the feed rate may beintroduced. By varying the feed rate (e.g., changing the feed rate by0.001 to 0.005 inches per revolution), the resulting chips will have avariable thickness that alternates between thin and thick sections. Thisvariable thickness will cause the chips to tend to break at the thinsections, and enable the remainder of the chip to be evacuated moreeasily. This method may be referred to as micro-peck drilling becausethe cutter (e.g., the bit) stays in the material and is always cutting achip. If the amplitude is increased to exceed the feed rate, thenmacro-peck drilling results in which the cutter is actually removed fromcontact with the material of the workpiece.

Micro-peck drilling methods that are currently employed typically usespecial thrust bearings that have oscillating cam profiles. However,these special thrust bearings are typically very expensive and havelimited life spans.

BRIEF SUMMARY OF SOME EXAMPLES

Some example embodiments may enable the provision of a positive feedtool that employs a different structure to employ micro-peck drillingwith an oscillating feed rate. In this regard, some example embodimentsmay provide a feed rate oscillator that employs variable pitch diametergears to generate the feed rate oscillation.

In an example embodiment, a positive feed tool is provided. The tool mayinclude a motor, a power supply operably coupled to the motor to powerthe motor, a gear head and a spindle. The gear head may be operablycoupled to the motor to be operated responsive to powering of the motor.The gear head may include a drive assembly and a feed assembly. Thespindle may be operably coupled to the gear head to enable the spindleto be selectively driven rotationally and fed axially based on operationof the drive assembly and the feed assembly, respectively. The feedassembly may include a feed rate oscillator having a spindle feed gearoperably coupled to a differential feed gear. The spindle feed gear isoperably coupled to rotate the spindle to selectively axially feed thespindle. The differential feed gear is selectively operably coupled toan input shaft turned by the motor. At least one of the spindle feedgear or the differential feed gear has a variable pitch diameter.

In another example embodiment, a gear head for selectively driving andfeeding a spindle of a positive feed tool is provided. The gear head mayinclude a drive assembly configured to selectively drive the spindlerotationally, and a feed assembly configured to selectively feed thespindle axially. The feed assembly may include a feed rate oscillatorhaving a spindle feed gear operably coupled to a differential feed gear.The spindle feed gear is operably coupled to rotate the spindle toselectively axially feed the spindle. The differential feed gear isselectively operably coupled to an input shaft turned by the motor. Atleast one of the spindle feed gear or the differential feed gear has avariable pitch diameter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described some example embodiments in general terms,reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, and wherein:

FIG. 1 illustrates a functional block diagram of a positive feed toolthat may employ a feed rate oscillator according to an exampleembodiment;

FIG. 2 illustrates a cross section view of a positive feed tool having afeed rate oscillator according to an example embodiment; and

FIG. 3A illustrates a top view of the feed rate oscillator havingnon-circular gears in accordance with an example embodiment;

FIG. 3B illustrates a top view of the feed rate oscillator havingalternatively shaped, non-circular gears in accordance with an exampleembodiment;

FIG. 4A illustrates a top view of gears with tooth profile modificationin accordance with an example embodiment;

FIG. 4B illustrates a top view of gears with tooth profile modificationin accordance with an alternative example embodiment;

FIG. 5 illustrates a comparison of change in feed rate versus degrees ofrotation in accordance with two example embodiments;

FIG. 6A shows a feed profile with a first frequency in accordance withan alternative example embodiment;

FIG. 6B shows a feed profile with a second frequency in accordance withan alternative example embodiment; and

FIG. 6C shows a feed profile with a third frequency in accordance withan alternative example embodiment.

DETAILED DESCRIPTION

Some example embodiments now will be described more fully hereinafterwith reference to the accompanying drawings, in which some, but not allexample embodiments are shown. Indeed, the examples described andpictured herein should not be construed as being limiting as to thescope, applicability or configuration of the present disclosure. Rather,these example embodiments are provided so that this disclosure willsatisfy applicable legal requirements. Like reference numerals refer tolike elements throughout. Furthermore, as used herein, the term “or” isto be interpreted as a logical operator that results in true wheneverone or more of its operands are true. As used herein, operable couplingshould be understood to relate to direct or indirect connection that, ineither case, enables functional interconnection of components that areoperably coupled to each other.

As indicated above, some example embodiments may relate to the provisionof highly capable positive feed tools that also have superiorcharacteristics relative to providing feed rate oscillation. Inparticular, some example embodiments may provide a positive feed toolhaving a feed rate oscillator that provides feed rate oscillation sothat chip formation can be controlled based on the geometry andstructure of the feed rate oscillator provided. Moreover, some exampleembodiments may provide a feed rate oscillator that employs variablepitch diameter gears. FIG. 1 illustrates a functional block diagram of apositive feed tool that may employ a feed rate oscillator according toan example embodiment.

As shown in FIG. 1, a positive feed tool 100 of an example embodimentmay include a motor 110, a power supply 120 and a gear head 130 that isconfigured to drive a spindle 140. The spindle 140 may be driven torotate about an axis and also be fed in a direction along the axis ofrotation to, for example, power a bit disposed at a distal end of thespindle 140 to drill a hole in a workpiece 150. In some cases, the motor110 or other components of the positive feed tool 100 may optionally beoperated under the control of an optional controller 160. Although notrequired, the gear head 130 may be fitted or mated with one or moreaccessories 170 that may augment or otherwise alter various capabilitiesor aspects of performance of the positive feed tool 100. The accessories170 may therefore be removable, exchangeable, or otherwise electivelyemployed for operation of the positive feed tool 100.

In some examples, the motor 110 may be a pneumatic motor, and the powersupply 120 may therefore be pressurized air. However, in alternativeembodiments, the motor 110 may be an electric motor or a hydraulicallypowered motor, and the power supply 120 would then be battery/mainspower or a hydraulic power supply, respectively. Regardless of how themotor 110 is powered, the motor 110 may be operably coupled to the gearhead 130 to drive and feed the spindle 140.

In an example embodiment, the motor 110 may be operably coupled to drivethe gear head 130 for rotation of the spindle 140 about an axis thereofvia a drive assembly 180. In some cases, the spindle 140 may be anelongated member having one or more slots for engagement with a drivegear of the drive assembly 180 to rotate the spindle 140 based onrotation of the drive gear. The spindle 140 may also include threads forengagement with a feed gear of a feed assembly 182 that is configured tofeed the spindle 140 in a direction along the axis of the spindle 140and into (or away from) the workpiece 150. Thus, for example, the driveassembly 180 and the feed assembly 182 may be operably coupled to themotor 110 (and/or each other) to enable selective drive and feeding ofthe spindle 140.

As mentioned above, if the feed assembly 182 is powered to generate aconstant feed rate (e.g., 0.003 inches per revolution), then the spiralshaped chips having a constant thickness will be generated, and variousproblems could result. Accordingly, to vary the thickness of the chips,and to facilitate breakage and more easy evacuation of the chips, anoscillating feed rate may be employed. To provide the oscillating feedrate, example embodiments may employ a feed rate oscillator 190 (orFRO), which may be operably coupled to or provided as a portion of thefeed assembly 182.

As may be appreciated from the description above, the specificcomponents of the gear head 130 can be varied in some cases. An examplestructure for the gear head 130 will be described in reference to FIG.2. However, other specific structures can be employed to embody portionsof the gear head 130 in some alternative embodiments. The structureemployed for certain portions of the gear head 130 may then impactcorresponding structures employed for the feed rate oscillator 190.

Referring now to FIG. 2, the gear head 130 may include a casing orhousing 200 inside which various components of the drive assembly 180and the feed assembly 182 may be housed. The motor 110 may be operablycoupled to the spindle 140 via a differential unit 210. The differentialunit 210 may include a differential drive gear 212 and a differentialfeed gear 214 that may engage a spindle drive gear 142 and spindle feedgear 144, respectively. The spindle drive gear 142 and spindle feed gear144 may each be operably coupled to the spindle 140 to selectivelyprovide drive and feed for the spindle 140. Meanwhile, the differentialdrive gear 212 and the differential feed gear 214 may each be operablycoupled to a feed shaft 216.

In an example embodiment, the spindle 140 may include one or more slotsfor engagement with the spindle drive gear 142 and threads forengagement with the spindle feed gear 144. The spindle drive gear 142and spindle feed gear 144 may each also have a generally annular shapewith a central opening to receive the spindle 140. Internal threadsprovided on the spindle feed gear 144 may engage external threads alongthe length of the spindle 140 so that when the spindle feed gear 144 isrotated in relation to the spindle 140, the spindle 140 will feed in anadvancing feed direction shown by arrow 220.

The differential drive gear 212 and the differential feed gear 214 eachextend around the feed shaft 216 and include gear teeth for engagementwith respective ones of the spindle drive gear 142 and spindle feed gear144. The differential feed gear 214 is operably coupled to the feedshaft 216 to move axially with the feed shaft 216. The differentialdrive gear 212 is operably coupled to the feed shaft 216, but does notmove axially with the feed shaft 216, instead having a central openingthrough which the feed shaft 216 slides.

When the motor 110 operates, an input shaft 230 is turned. A set ofbevel gears 232/234 then translates the rotation of the input shaft 230to input gear 240. Another gear 250 is operably coupled to the inputgear 240. The input gear 240 is operably coupled to the differentialunit 210 (e.g., via the differential drive gear 212. The differentialdrive gear 212 and the differential feed gear 214 may be selectivelyoperably coupled to each other to cause the differential feed gear 214to either rotate with the differential drive gear 212 (e.g., when thedifferential drive gear 212 and the differential feed gear 214 areengaged) or not rotate with the differential drive gear 212 (e.g., whenthe differential drive gear 212 and the differential feed gear 214 arenot engaged). The spindle drive gear 142 will generally be driven by thedifferential drive gear 212 when the motor 110 operates and rotate thespindle 140. However, the spindle feed gear 144 is only driven when thedifferential feed gear 214 is engaged with the differential drive gear212. When the differential feed gear 214 is disengaged from thedifferential drive gear 212, both the differential feed gear 214 and thespindle feed gear 144 become stationary. The rotation of the spindle 140while the spindle feed gear 144 is stationary then resultantly causesthe spindle 140 to be withdrawn and move in a direction opposite theadvancing feed direction shown by arrow 220.

In a typical configuration, the feed rate generated by the operationdescribed above would be a constant feed rate (e.g., of about 0.003inches per revolution). Similarly, in some typical configurations, thedifferential feed gear 214 and/or the spindle feed gear 144 may eachhave a round, and perhaps cylindrical, profile so that the constant feedrate is maintained. However, in accordance with an example embodiment,the feed gear pitch diameter of one or both of the differential feedgear 214 and the spindle feed gear 144 can be modified over at least aportion thereof in order to change the feed rate from the constant feedrate to an oscillating feed rate. In some cases, the pitch diameter ofthe differential feed gear 214 and/or the spindle feed gear 144 can bemodified to change the ratio of the gears as they rotate to provide theoscillating feed rate. Thus, in accordance with an example embodiment,the feed rate oscillator 190 of FIG. 1 may be embodied in thedifferential feed gear 214 and/or the spindle feed gear 144 and thestructural modifications employed on the differential feed gear 214and/or the spindle feed gear 144 to produce the variations in pitchdiameter.

The pitch diameter of the differential feed gear 214 and/or the spindlefeed gear 144 can be varied by multiple different methods. One examplemethod may include employment of non-circular gears. For example, eachof the differential feed gear 214 and the spindle feed gear 144 may beformed as non-circular feed gears to result in a changing gear ratio asthe gears rotate. An alternative example method may employ circulargears with profile modifications over a prescribed portion of such gearsto create a changing pitch diameter and gear ratio as the gears rotate.Still another alternative method may include a combination of employingnon-circular gears and profile modifications for changing pitchdiameter. In some cases, this combined approach may generateopportunities for improved performance and adjustability.

In accordance with the first example described above, both the spindlefeed gear 144 and the differential feed gear 214 may be non-circular.FIG. 3A illustrates an example in which a top view of a non-circularspindle feed gear 300 and a non-circular differential feed gear 310 areemployed. As can be appreciated from FIG. 3A, the non-circular spindlefeed gear 300 and the non-circular differential feed gear 310 each havean oval shape in this example. Feed rate, amplitude and frequency can bechanged by changing the shapes of one or both gears. As an example ofanother shape that could be employed, FIG. 3B shows a rectangularspindle feed gear 320 and a rectangular differential feed gear 330.Again, the feed rate, amplitude and frequency can be changed by changingthe shapes of one or both gears. Mixed shapes could also be employedbetween the spindle feed gear 144 and the differential feed gear 214.

As described above in reference to the first alternative method in whichpitch diameter changes are achieved by profile modifications, one orboth feed gears may be modified to have varying pitch diameters.Provision of varying pitch diameters may be accomplished by performingtooth profile modification on one or both feed gears. In one embodiment,the spindle feed gear 144 may be provided with an oscillating gear toothprofile and the differential feed gear 214 may be provided with aconstant tooth profile. In other words, the density of teeth around theperiphery of the differential feed gear 214 may be consistent about theentire periphery of the differential feed gear 214. However, the densityof teeth around the periphery of the spindle feed gear 144 may changewith a cyclic increase and decrease in density being provided as theperiphery of the spindle feed gear 144 is traversed. Of course, inanother example embodiment, this approach may be reversed and thespindle feed gear 144 may have a constant tooth profile while thedifferential feed gear 214 has the oscillating gear tooth profile. Instill another example embodiment, both the spindle feed gear 144 and thedifferential feed gear 214 to have oscillating tooth profiles.

FIG. 4A illustrates an example representation of a differential feedgear 400 with a constant tooth profile in which a region 402 having afirst tooth density extends around the entire periphery of thedifferential feed gear 400. Meanwhile, a spindle feed gear 410 isprovided having an oscillating tooth profile by virtue of the fact thata first region 412 has a higher tooth density than a second region 414,which has a higher tooth density than a third region 416. The first,second and third regions 412, 414 and 416 may alternate around theperiphery of the spindle feed gear 410.

FIG. 4B illustrates a reverse of the situation described in FIG. 4A. Inthis regard, a spindle feed gear 420 is provided with a constant toothprofile in which a region 422 having a predefined tooth density extendsaround the entire periphery of the spindle feed gear 420. Meanwhile, adifferential feed gear 430 is provided having an oscillating toothprofile by virtue of the fact that a first region 432 has a higher toothdensity than a second region 434, which has a higher tooth density thana third region 436. The first, second and third regions 432, 434 and 436may alternate around the periphery of the differential feed gear 430.

In the examples of FIGS. 3A, 3B, 4A and 4B, one or both of the gears maybe replaced to change feed rate, frequency, or amplitude. As such, insome cases, the gears may be examples of the accessory 170, and theoperator may employ gears having the desired characteristics to achievefeed rate oscillation that is preferred for a given material orsituation.

In example embodiments in which any of various combinations of theexamples of FIGS. 3A, 3B, 4A and 4B are employed, one or both gears mustbe replaced to adjust feed rate and frequency; however, the amplitude isdependent on the timing between the two gears. The amplitude can beadjusted by changing which teeth are mating. For example, if the peak ofone gear is meshed with the valley of the other gear, the resulting wavemay be similar to curve 500 in FIG. 5. If those same two gears areinstalled so that the peaks of both gears are meshed the resulting wavemay be similar to curve 510 in FIG. 5.

The chart of FIG. 5 shows two example amplitudes, but there are multipleamplitudes in between these. Each time the gear mesh is shifted onetooth, the amplitude changes slightly. Therefore, the limiting factor onnumber of adjustments is determined by the number of teeth in the gear.This provides a very high level of amplitude adjustability, and suchadjustability provides for a fine level of detail that can be achievedfor adjustability (i.e., down to the individual tooth level). Thisadjustability and the capability for “tuning” the oscillation amplitudemay provide advantages for dealing with different levels of stiffness ofthe attachment nose, material being drilled, mounting fixture, cutter,etc.

While the feed rate varies during a single rotation of one of the gears,the averaged feed rate remains constant (e.g. 0.003″) throughout theprocess. The number of oscillations per revolution can be one, two,three, four, or as high as the number of teeth and gear size will allow.This method can also be used to make intermediate ratios such as 1.5,2.5, 3.5 etc. oscillations per revolution. Although the pitch diametersof belt pulleys, chain sprockets, and other similar transmissions canalso be varied to accomplish the same task without the use of gearing,variable pitch drive gears can be utilized to perform this oscillationin example embodiments. However, due to the resulting speed oscillation,varying the feed gears may be appreciated as one example way toaccomplish variable pitch diameters.

FIG. 6, which includes FIGS. 6A, 6B and 6C, illustrates three chartsshowing examples of different oscillations per revolution. In thisregard, FIG. 6A shows a feed profile 600 with an average feed rate of0.0033 inches per revolution, amplitude of 0.006 inches, and a frequencyof 1.0. FIG. 6B shows a feed profile 610 with an average feed rate of0.0033 inches per revolution, an amplitude of 0.006 inches, and afrequency of 2.0. FIG. 6C shows a feed profile 620 with an average feedrate of 0.0033 inches per revolution, an amplitude of 0.006 inches, anda frequency of 3.0. An oscillation of one per revolution, as shown inFIG. 6A, can therefore result in a chip that is one diameter long. Twooscillations per revolution, as shown in FIG. 6B, may create chipsone-half a diameter long. Three oscillations per revolution, as shown inFIG. 6C, may create chips one-third of a diameter long, etc. In theseexamples, the frequency changes but the feed rate and the amplituderemain constant.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Moreover, although the foregoing descriptions and the associateddrawings describe exemplary embodiments in the context of certainexemplary combinations of elements and/or functions, it should beappreciated that different combinations of elements and/or functions maybe provided by alternative embodiments without departing from the scopeof the appended claims. In this regard, for example, differentcombinations of elements and/or functions than those explicitlydescribed above are also contemplated as may be set forth in some of theappended claims. In cases where advantages, benefits or solutions toproblems are described herein, it should be appreciated that suchadvantages, benefits and/or solutions may be applicable to some exampleembodiments, but not necessarily all example embodiments. Thus, anyadvantages, benefits or solutions described herein should not be thoughtof as being critical, required or essential to all embodiments or tothat which is claimed herein. Although specific terms are employedherein, they are used in a generic and descriptive sense only and notfor purposes of limitation.

That which is claimed:
 1. A positive feed tool comprising: a motor; apower supply operably coupled to the motor to power the motor; a gearhead operably coupled to the motor to be operated responsive to poweringof the motor, the gear head comprising a drive assembly and a feedassembly; and a spindle operably coupled to the gear head to enable thespindle to be selectively driven rotationally and fed axially based onoperation of the drive assembly and the feed assembly, respectively;wherein the feed assembly comprises a feed rate oscillator comprising aspindle feed gear coupled to a differential feed gear, the spindle feedgear being carried on the spindle to rotate the spindle to selectivelyaxially feed the spindle, the differential feed gear being carried on afeed shaft and being selectively operably coupled to an input shaftturned by the motor; wherein at least one of the spindle feed gear orthe differential feed gear is a variable pitch diameter gear having avariable pitch diameter; wherein the variable pitch diameter gearincludes an oscillating gear tooth profile to provide the variable pitchdiameter, the oscillating gear tooth profile comprising a plurality ofregions, each region having a first tooth density, a second toothdensity, or a third tooth density and the regions being disposed arounda periphery of the variable pitch diameter gear in accordance with atooth density pattern, wherein the first tooth density is greater thanthe second tooth density and the second tooth density is greater thanthe third tooth density, and wherein the tooth density pattern defines arepeating sequence of adjacent regions having the second tooth densityadjacent to the first tooth density adjacent to the second tooth densityadjacent to the third tooth density.
 2. The positive feed tool of claim1, wherein the spindle feed gear or the differential feed gear is anon-circular gear.
 3. The positive feed tool of claim 1, wherein thespindle feed gear and the differential feed gear each includenon-circular gears.
 4. The positive feed tool of claim 1, wherein thespindle feed gear and the differential feed gear each include theoscillating gear tooth profile.
 5. The positive feed tool of claim 1,wherein the spindle feed gear and the differential feed gear eachinclude an oscillating gear tooth profile and are non-circular gears. 6.The positive feed tool of claim 1, wherein feed rate oscillationprovided by the feed rate oscillator is tunable by an operator of thepositive feed tool.
 7. The positive feed tool of claim 6, wherein anamplitude of the feed rate oscillation is adjustable by adjusting analignment of teeth between the spindle feed gear and the differentialfeed gear.
 8. The positive feed tool of claim 1, wherein the spindlefeed gear or the differential feed gear is replaceable to alter feedrate, frequency or amplitude.
 9. The positive feed tool of claim 1,wherein a number of oscillations per revolution is adjustable bychanging gear size or tooth profile.
 10. A gear head for selectivelydriving and feeding a spindle of a positive feed tool, the gear headcomprising: a drive assembly configured to selectively drive the spindlerotationally; and a feed assembly configured to selectively feed thespindle axially; wherein the feed assembly comprises a feed rateoscillator comprising a spindle teed gear coupled to a differential feedgear, the spindle feed gear being carried on the spindle to rotate thespindle to selectively axially feed the spindle, the differential feedgear being carried on a feed shaft and being selectively operablycoupled to an input shaft turned by the motor; wherein at least one ofthe spindle feed gear or the differential feed gear is a variable pitchdiameter gear having a variable pitch diameter; wherein the variablepitch diameter gear includes an oscillating gear tooth profile toprovide the variable pitch diameter, the oscillating gear tooth profilecomprising a plurality of regions, each region having a first toothdensity, a second tooth density, or a third tooth density and theregions being disposed around a periphery of the variable pitch diametergear in accordance with a tooth density pattern, wherein the first toothdensity is greater than the second tooth density and the second toothdensity is greater than the third tooth density, and wherein the toothdensity pattern defines a repeating sequence of adjacent regions havingthe second tooth density adjacent to the first tooth density adjacent tothe second tooth density adjacent to the third tooth density.
 11. Thegear head of claim 10, wherein the spindle feed gear or the differentialfeed gear is a non-circular gear.
 12. The gear head of claim 10, whereinthe spindle feed gear and the differential feed gear each includenon-circular gears.
 13. The gear head of claim 10, wherein the spindlefeed gear and the differential feed gear each include the oscillatinggear tooth profile.
 14. The gear head of claim 10, wherein the spindlefeed gear and the differential feed gear each include the oscillatinggear tooth profile and are non-circular gears.
 15. The gear head ofclaim 10, wherein feed rate oscillation provided by the feed rateoscillator is tunable by an operator of the positive feed tool.
 16. Thegear head of claim 10, wherein maximum amplitude of the feed rate of thespindle is adjustable by reinstalling one of the spindle feed gear orthe differential feed gear in an adjusted alignment with the other ofthe spindle feed gear and the differential feed gear.
 17. The gear headof claim 10, wherein a number of oscillations per revolution isadjustable by changing gear size or tooth profile.